Permethrin is a synthetic pyrethroid which exhibits repellent as well as knockdown and kill activity against insects. Pyrethroids, including both the naturally occurring compounds and their synthetically prepared analogs effectively control a variety of pests, such as ticks, cockroaches, houseflies, mosquitoes, black flies, fleas, and other flying or crawling insects. Pyrethroids are not harmful to plants, food, animals or humans, and leave no harmful residues.
Despite these highly favorable characteristics, permethrin has had only limited general utility because of its relatively short-lived insecticidal activity. This is due to the decomposition of permethrin into a nonactive, non-insecticidal product in the presence of oxygen and ultraviolet light.
U.S. Pat. No. 5,198,287 issued Mar. 30, 1993 to Samson, et al. for INSECT REPELLENT TENT FABRIC discloses a tent fabric with a water repellent and flame retardant coating that includes the insecticide permethrin. The patent teaches that placing the permethrin in the coating on the inner surface of the tent enables the tent fabric and outer surface coating to shield the permethrin from oxygen and ultraviolet light and thereby provide an effective life of more than six months for the permethrin.
U.S. Pat. No. 5,252,387 issued Oct. 12, 1993 to Samson for FABRICS WITH AN INSECT REPELLENT AND A BARRIER teaches that permethrin can be preserved in insect repellent fabrics by placing a barrier over the permethrin to protect the permethrin from degradation by ultraviolet light and oxygen.
Another problem with using permethrin as an insect repellent in washable clothing is retaining the permethrin in washable garments through successive wash cycles.
U.S. Pat. No. 5,089,298 issued Feb. 18, 1992 to McNally for SYNERGISTIC EFFECT OF AMYLOPECTIN-PERMETHRIN IN COMBINATION ON TEXTILE FABRICS offers one solution to the problem of retaining permethrin in clothing through successive wash cycles. McNally teaches that permethrin is retained in garments impregnated with permethrin and amylopectin, a water soluble form of starch, through a substantially greater number of laundering cycles than garments treated only with permethrin.
Applicants' parent application, Ser. No. 08/401,986, teaches that an initial concentration in a fabric of approximately 1.25 grams of permethrin per square meter is strong enough to repel insects. The '986 application also teaches that the addition of polyvinyl acetate as a binder for the permethrin dispersion preserves the effectiveness of the permethrin through more washings of the fabric than does McNally's amylopectin.
Applicants' research has continued for effective use of permethrin in repelling mosquitoes and other insects, and applicants have found polymeric binders other than the polyvinyl acetate disclosed in our parent '986 application to be effective in prolonging the durability of permethrin. Applicants have also found a process of applying permethrin to the fabric that effectively increases the repellency of insects and that maintains the effectiveness of permethrin after repeated launderings of the treated fabric.